This invention relates to a flap actuator system for an airfoil structure.
During steady, level, forward flight in a helicopter, the air velocity vector relative to the blade varies with blade azimuthal position in a complex, yet predictable, manner. In general, the result is a varying lift pattern that is periodic with a multiple of rotor rotation rate. The intensity and time dependence of this force is related to the forward velocity of the helicopter, wind conditions, blade instantaneous angle of attack, blade dynamics and aeroelastic properties, and rotor speed. These lift variations bend the blades up and down every revolution and produce a harmonic series of vibrations and noise synchronized to the blade rotation rate. When a helicopter is descending or leaning into a turn, additional noise and vibration are generated by even more complex lift variations caused by blades flying through wakes and trailing vortices of other blades. Other complex excitation sources include atmospheric turbulence, fuselage interference, and mismatches in airfoil aerodynamic and/or aeromechanical properties.
To compensate or minimize these time dependent forces, helicopters and vertical lift aircraft have controlled surfaces or variable angle-of-attack blades. A controlled surface flaps up and down to produce a twist moment or change the instantaneous lift of the blade or wing. The control surface could consist of the entire blade or a flap on the trailing edge of a blade or wing. A change in lift caused by the actuation of a flap acts as a canceling force, neutralizing vibrations produced by the unequal lift on different blades.
In this prior art, most helicopters vary the angle of attack of the blade at 1/rev by means of a conventional swash plate to minimize the 1/rev blade harmonic. Other production helicopters use a blade-mounted trailing flap modulated at 1/rev for this purpose. The upper harmonics and non-synchronized lift variations are not, in general minimized due to the mechanical complexity of such high frequency actuation.
For rotor blade mounted flaps, several techniques are known for actuation of a flap. Kaman actuates a servo flap via a long rod, which twists a blade once per revolution. Others have used a cable to pull a mechanism to move the flap. These mechanical methods are generally reliable, but are unsuitable for higher harmonic blade control. They suffer from slow response, backlash, and programming inflexibility should desired flap schedule or harmonic content requirements change. Hydraulic systems are capable of generating large force and considerable stroke. However, they are heavy, usually limited in frequency response, and less reliable at the high repetition rate required of the actuator.
Piezoelectric or xe2x80x9csmart materialxe2x80x9d devices, used in research for a decade, offer fast response and light weight. As a voltage is applied to the piezoelectric crystal, it swells a few thousandths of an inch. The swelling drives a leveraged system that amplifies its stroke. Smart material actuators suffer from low torque and power capability, and generally, small strokes. Though amplifying the strokes mechanically increases flap deflection angle, this is offset by torque reduction, weight increase, introduction of backlash, and inherent reduced reliability. Piezoelectric actuator research continues, further improvements are possible, but the drawbacks mentioned above still appear to represent a serious roadblock to their practical implementation in production helicopters.
It is therefore an object of this invention to provide an improved flap actuator system for controlling an airfoil structure.
It is a further object of this invention to provide a system which provides increased power and torque.
It is a further object of this invention to provide a system which has more of its weight forward on a rotating blade.
It is a further object of this invention to provide an improved flap actuator system which is electrically operated, simple and rugged.
It is a further object of this invention to provide an improved flap actuator system which is powerful, robust and lightweight.
It is a further object of this invention to provide an improved flap actuator system which reduces vibration and noise.
It is a further object of this invention to provide an improved flap actuator system which improves lift.
It is a further object of this invention to provide an improved flap actuator system which is capable of operating quickly and at high g loads.
It is a further object of this invention to provide an improved flap actuator system which can be located at significant radial distances on a rotating blade where small movements produce substantial aerodynamic forces.
The invention results from the realization that a truly simple and effective flap actuator system capable of operating quickly and in high g environments can be achieved by employing an electromagnetic motor whose armature and field are made integral with the flap member and airfoil structure so that they themselves become part of the motor or motor segment, and the further realization that an intermediate drive mechanism could also be used between the motor and flap so that the motor is integral with the airfoil structure and drive mechanism, and the further realization that the flap can be suspended from the airfoil structure by a tension member.
This invention features a flap actuator system for an airfoil structure including a flap member for controlling the airfoil structure. A bearing member interconnected with the flap member and the airfoil structure. Also included is an actuator device for rotating the flap member about the bearing member relative to the airfoil structure, the actuator device including an electromagnetic motor segment and a drive mechanism driven by the electromagnetic motor to rotate the flap member about the axis of the bearing member relative to the airfoil structure. The electromagnetic motor is integral with the airfoil structure and the drive mechanism. The electromagnetic motor includes a field circuit integral with the drive mechanism and an armature circuit integral with the airfoil structure, the field circuit being located within the armature circuit.
The drive mechanism may include a pulley drive, a lever drive, a gear device, a crossband drive, or a rigid link.